The cilia of the mammalian respiratory tract are involved in tracheobronchial clearance. In order to understand the precise role cilia play in mucous transport it is first necessary to isolate the events and the regulation of those events which are due to ciliary activity from other physiological responses. For this purpose 3 model in vitro systems are being developed. These utilize small groupings of ciliated cells (3-5 cells), single cells or isolated demembranated, ATP-reactivated cilia from the trachea of rabbits. Ciliary beat patterns and metachronism will be quantified by using high-speed cinematography, a projector for single-frame advance and a GRAF-PEN interface to a minicomputer. These data will be correlated with morphological information obtained by transmission and scanning electron microscopy. Once normal parameters for ciliary activity are obtained, we will assess the effects of hormones, ions and drugs on ciliary function, free of other physiological events. Ultimately, such information will allow us to interpret ciliary activity in quantitative terms in other multiciliated tissues.